The present invention relates to improvements in electronic countermeasure techniques and more particularly to new and improved techniques for electronic deception of a lobing radar. In the field of electronic warfare it has been general practice to use a modulated beam of repeater pulses to return a deception signal to the angle-tracking circuits of a lobing radar. The success of such techniques has been dependent on the type of radar used, the power available, and the ability to determine scan frequencies of the radar. Particular problems have been encountered in deceiving missiles equipped with COSRO (conical scan on receive only) radar.
In order to deceive a COSRO radar, a signal near the scan frequency must be used to modulate a repeater pulse train to form an envelope detected by the angle-tracking circuits (elevation and azimuth) of the scanning radar. Since the COSRO radar, as is well known, does not disclose its precise scan frequency, the modulation signal must cover a range of expected scan frequencies of the radar.
One method presently used and known as "swept audio" employs, in a particular embodiment, repetitive linear ramp upsweep from 60-80 Hz. The 60-80 Hz range is used against those COSRO homing missiles which employ an approximately 70 Hz scan frequency. A repetitive downsweep or a repetitive triangular sweep, that is, an upsweep followed by a downsweep, may also be used. By sweeping the modulating frequency through the 60-80 Hz range many times during a period of radar tracking, it was believed that successful jamming could be accomplished. However, an analysis of the "swept audio" technique has shown that power is only concentrated in specific frequencies which only by chance may be near the scan frequency as required.
Accordingly, the present invention has been developed to overcome the specific shortcomings of the above known and similar techniques and to make better use of the RF (radar frequency) power and time available for jamming and deceiving the angle-tracking circuits of the lobing radar.